The inventive concepts described herein relate to a semiconductor memory device, and more particularly, to a storage device including a nonvolatile memory device and a read method thereof.
Semiconductor memory devices may be characterized as volatile or nonvolatile. Although volatile semiconductor memory devices may perform read and write operations at high speed, content stored within volatile semiconductor memory devices may be lost at a power-off condition. In contrast, nonvolatile semiconductor memory devices are characterized by the retention of stored content regardless of whether or not they are powered.
Flash memory devices are an example of typical nonvolatile semiconductor memory devices. Flash memory devices may be widely used as voice and image data storing mediums of information appliances such as computers, cellular phones, PDAs, digital cameras, camcorders, voice recorders, MP3 players, handheld PCs, game machines, facsimiles, scanners, printers, and the like.
As the demand for mass storage devices increases, multi-level cells (MLCs) or multi-bit memory devices which store multiple bits per cell are becoming widely used. However, in memory devices employing multi-level cells, the threshold voltages of the memory cells may be identified as any of a plurality of states within a restricted voltage window. The threshold voltage of memory cells typically will vary with characteristics of the memory device, the lapse of time, and/or peripheral temperature. As a result, read voltages for identifying data states of the multi-level cells need to be adjusted to improve data integrity.